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Bike maintenance - John C. Kirk

Sep. 9th, 2009

04:55 pm - Bike maintenance

Back in 1998, I bought a mountain bike. For a while, I used it to cycle to work, but I got a bit frustrated because I kept getting punctures from all the broken glass on the road. I think this mostly comes from beer bottles rather than broken car lights; for instance, my upstairs neighbours woke me up at 04:30 on Saturday morning when they were throwing their empty bottles out of the window to shatter all over the road.

So, when I bought my Brompton last year, I opted for Schwalbe Marathon tyres, which are reinforced with Kevlar. I've been impressed by these, so I've recommended them to several other people; 10 months after I started riding the new bike, I hadn't had a single puncture. Unfortunately, I've had a bit of a bad run of luck in the last week.

Last Wednesday, I was just outside my office building (on my way into work), when my front tyre went from full to flat in a couple of seconds. I wasn't stranded, since I could just carry the bike inside, but I didn't have a spare tube or any tools with me. In fact, I'd neglected to buy any spare inner tubes, and my basic theory was that it would always be simplest to fold up the bike and carry it home rather than making roadside repairs. (I'm now reconsidering that theory; it's ok if I'm on my way home already, but less convenient if I'm on my way somewhere else.) Anyway, I carried the bike home on Wednesday evening, then bought a travelcard on Thursday so that I could get into work and buy a replacement inner tube. I went to the Evans near Victoria, and it turned out that the inner tubes are significantly cheaper than on their website (£2.71 vs £4.99), so I bought two: one for the immediate problem, and one as a spare.

I should have replaced the tube when I got home on Thursday evening, but I procrastinated; ditto on Friday evening, so this wound up costing me about £20 in extra travel costs. I finally got around to tackling it on Saturday afternoon. The main problem was that I lacked confidence. I looked at the bike and thought "Urk, I don't know how to do this. Bike maintenance is hard; let's watch TV!" My old mountain bike had a "quick release" front wheel, so it was very easy to remove: just unhook the brake pads, twist a couple of levers, then it was out. (The trade-off is that this also makes it easier for thieves to separate the wheel from the rest of the bike.) With the Brompton, it's more involved, particularly if you have a hub-dynamo. Quoting from the manual:

For a front wheel with hub-dynamo, undo the long M5 bolt (4mm hex-key), and withdraw it: on the LH side there is a "nut" (with plastic cover) and you may have to hold this to stop it rotating. Move the hook (and mudguard stay) out of the way, and detach the special LH tab washer. Retain the special spacer and tab-washer on the RH side.

I went online to try to find more information, but this was a dead end. For instance, this page says: "Front wheel punctures are easy on the Brompton, so I'll concentrate on the back wheel".

It took me about an hour for the whole process, but it should be quicker in future, now that I know what I'm doing. I'll document the process with photos at some point, but in the meantime I have to mention one key step that's missing from the instructions. Take a look at this picture of the front wheel. On the near side, there's a double black cable connected to the centre of the wheel. The manual doesn't mention this, so I assumed that this was part of the "special spacer" that had to be retained. However, that meant that I couldn't remove the wheel completely, and it was a bit fiddly trying to get the tyre off. It turns out that those black cables simply slide out of the hub: I discovered this by accident while I was grappling with the wheel. After that, I could remove the wheel completely, which made the job much easier! The instructions didn't say anything about the brakes, so I left them alone; since the tyre was flat, it easily squeezed through the gap.

I have some metal tyre levers, which are L-shaped, and initially I wasn't sure which end I was supposed to put in. However, I found some useful advice online: there's a notch near the end of the long bit, and you can hook that onto one of the wheel spokes to keep the lever in place while you sort out the next one. (These are the same levers that I used on my old mountain bike, but I don't think I ever used that notch.) Another useful tip is to check the inside of the tyre to see whether the thing that caused the puncture is still present. In this case, there was a sliver of glass still stuck in there, so I removed that. It really was tiny, though: smaller than one of my fingernail clippings. The inner tube was still intact, and it was easy to find the hole (I just reinflated the tube then heard/felt the air rushing out), so I lined up the tube with the tyre to give me a starting point. When Brompton built the bike, they lined up the blue Schwalbe logo with the valve, which looks neat and makes it easier to get your bearings, so I did the same thing when I replaced the tyre.

The manual mentions various torque settings for the bike. For instance, when I replaced the handlebar catch recently, that should be attached at 9Nm (Newton metres). Similarly, the bolt on the front wheel should be 6Nm (for a dyno-hub). However, you need a torque wrench to measure torque, and I don't have one; they're also quite expensive (at least £30). In fact, you probably need more than one, to measure different ranges, in the same way that kitchen scales are different to bathroom scales, and that raises the price even further. So, I just used a normal hex key for these, and took a rough guess at how tight it ought to be (based on how much force I had to use to undo it). It's tricky, though: too much force and you'll damage it, but not enough force and the wheel will fall off. Still, Sheldon Brown would probably approve.

Once I'd finished, I took the bike out for a quick test ride, just around the block. That went fine, i.e. the tyre stayed fully inflated, although it did feel a bit weird. It's hard to describe, but the front felt a bit "thinner" than usual; I think I had the same reaction that other people have when they try out a Brompton for the first time, and are surprised by the small wheels. Later, I realised what it was: I normally have my bag attached to the front of the bike, but in this case I didn't bother (I just put my keys in my pocket), so that meant that the front was lighter than usual, and the bike felt a bit more "whippy".

On Sunday, I cycled up to SJA HQ, and left the bike there while I took the ambulance out on duty. Afterwards, I carried the bike out to the carpark to cycle home, and again I noticed that something felt different, but I couldn't quite identify what it was. When I unfolded the bike and sat on it, it definitely felt different: I looked down, and it turned out that my rear tyre was flat. Again, I can identify the weird feeling with hindsight: when I pick up the folded bike, gripping the main tube, the backs of my fingers are resting against the rear tyre. I'm used to this being fairly solid, so it felt different when the tyre was flat (either it felt squidgy or it wasn't sticking up far enough to touch my fingers at all). So, I need to start paying more attention to these feelings: if something feels different, stop and work out why!

At least this happened on my way home, so it only affected me. I brought the bike home on the bus, then went back to the manual. I also referred back to the websites that I'd previously dismissed as irrelevant; in particular, I recommend The Definitive Brompton Tire Change Manual. I also watched this YouTube video: Zen & the art of Brompton Maintenance, Part 1, which has some useful tips, although you can't really see the details of what he's doing. Again, I spent a while procrastinating, because the gear mechanism makes the rear wheel look quite complicated. I considered taking it into Evans on Monday morning: according to their workshop price list, they charge £25 to fix a rear puncture if you use hub gears (which I do). However, there are other complications linked to that, e.g. I have to delay my journey into work (potentially on two consecutive days) and pay for another travelcard. In the end, I figured that I should at least make an attempt; if I completely botched it, I could still just fold the bike and carry it in, so I wouldn't be any worse off.

I started at about 23:45 on Sunday evening and finished at about 01:15 on Monday morning, i.e. it took me 1½ hours. (This job involved a normal wrench rather than a hex key.) As with the front wheel, most of that time was spent staring at the bike or referring back to the instructions, rather than actually doing stuff. So, future attempts should be a lot quicker, although this is still something I'd prefer not to do at the roadside. I think that a workstand would make life easier; for the chemists amongst you, these are like giant retort stands, so you clamp the bike and hold it in the air. Balancing the Brompton upside down is a bit unstable because the gear change lever sticks up from the handlebars, and I have to bend down or sit on the floor to do the work. However, that's an extra expense, so I'll leave it for now.

When I got the rear inner tube out, it was harder to find the hole, so I had to take the old fashioned approach by pumping it up and then putting it in the kitchen sink (to see where the bubbles rose up through the water). I checked the tyre, but I couldn't find anything in there. I left the old tube inflated overnight, and after 9 hours it was still holding its shape (although it was thinner), so I'm guessing that my weight made it go flat a bit faster on Sunday. Anyway, I put a new inner tube onto the rear wheel. There's a blue piece of plastic that runs around the metal wheel (front and rear), and this has a hole for you to put the valve through. However, I found that I could only get the valve through it when I lifted the blue plastic away from the wheel; otherwise, the valve got stuck, because the holes in the plastic/metal didn't quite line up properly. I've kept both old inner tubes; I'm not planning to patch them, but I'd like to try cycling barefoot at some point, and if I wrap them around the pedals then I won't have to deal with spiky edges.

I cycled into work on Monday morning, and both tyres were fine; I've now started checking them each time I reach my destination. However, I had some trouble with the gears, as I described last week. This time, though, I was able to solve the problem myself. I knew what I'd done to the gear adjustment cable when I took it apart, so there weren't that many possibilities for mistakes. Basically, the knurled lock nut moves along the lower half of the chain, then the barrel screws the top half onto the bottom half until it meets the lock nut. The lock nut and barrel were touching each other when I started, so all I had to do was unscrew the barrel, try a different position for the lock nut, then screw the barrel up again, and I got it right on my first attempt. So, that's the real benefit of doing this type of maintenance myself: I learn skills so that I'm a bit more self-sufficient, and that will certainly be useful if I do any kind of cycle touring in the future.

On Monday evening my chain came off the front cog; annoying, but probably a coincidence (I think it happened once before), and easy enough to fix. Yesterday everything was fine for both journeys (to/from work). This morning I was cycling to the station and I noticed an odd noise; it reminded me of the clicky things that people used to put on their bikes when I was a kid, that would knock against the spokes as the wheel turned. Then I heard a loud bang, and the rear tyre went flat. I assume that this was the new inner tube exploding, as Michael predicted. Fortunately I was on a quiet road at the time, but I couldn't carry on to the station, and I didn't have any more inner tubes at home, so I went to the Croydon branch of Evans instead. I asked them to replace the rear tyre at the same time as the inner tube, since I knew that would need to be done sooner or later. This worked out quite nicely, since they charged me the same amount for labour; that makes sense, since they had to take the old tyre off anyway, and it's no extra work to put a new tyre on. Also, they only charged me £20 for labour; that's cheaper than it says on the website, and I did clarify that I have hub gears, but the guy didn't think that would be a problem. Anyway, they did a good job with that (they pumped the new tube up fully and fixed a separate problem with the brake pad alignment), and the new tyre looks a lot better than the old one; aside from the lack of sidewall damage, the treads are also deeper. It took about an hour for them to do the work, so I wandered around Croydon while I waited, and extended my mental map a bit (I found a footpath/cyclepath that isn't on my A-Z). I called in to work and took today as a "duvet day" (i.e. annual leave at short notice), so that's all worked out nicely.

Meanwhile, I was cycling home on Monday evening, and as I approached a few guys they started laughing. I initially assumed that they were mocking the bike, but then one of them said "I thought it was a car, bruv." Presumably that's because they saw the sweep of my headlight as I came around the corner, before they saw my bike, so that's a good endorsement; even if I can see where I'm going without the light, it makes me more visible to other people.

Comments:

FWIW, the bit of plastic inside the wheel rim is called "rim tape". it prevents the rough bits where the spokes attach to the rim from causing punctures. Also, rather than replacing your tube every time you have a puncture, I recommend getting some of these. They're real easy to use, and they seem to work - at least they have for me.

One think to watch when you change inner tubes (and I think this is what happened to you) is to ensure that the rubber innter tube doesn't get "pinched" between the wheel rim and the tyre - this causes lots of stress on the inner tube and leads to it bursting - sometimes it will burst as soon as you inflate the tyre, and sometimes when the tyre's under load.

Was their obvious damage to your rear tyre - i.e. could you see what caused the tube to explode?

I didn't see the old inner tube after the bang, and the tyre looked much the same as before (i.e. damaged in several places). When I changed the tube on Sunday, I did have some trouble getting the bead of the tyre to go in properly (so that it wasn't pinching the tube), and that may have been what went wrong; that's partly why I asked them to do the replacement for me yesterday.